This invention relates generally to improved heat transfer by heat transfer tubes in a heat recovery steam generator of a combined cycle power plant. More particularly, this invention relates to deformations in the outer surface of the heat transfer tubes to enhance heat transfer within a heat recovery steam generator, while also decreasing pressure drop within the heat recovery steam generator.
Combined cycle power plants include a heat recovery steam generator for recovering heat from the exhaust of a gas turbine to generate heat for powering a steam turbine, as is known. The heat recovery steam generator currently utilizes a plurality of tubes that transfer thermal energy from the gas turbine exhaust to water/steam inside the tubes thereby generating steam or boosting steam temperature. The tubes have solid serrated fins to promote heat transfer. Water/steam within the tubes is heated by the passing exhaust gases to generate steam or super heated steam for powering the steam turbine of the combined cycle power plant. However, a pressure drop occurs on the air side of the heat recovery steam generator, which adversely impacts performance of gas turbines. Increasing the number of fins to improve heat transfer at the tubes, may result in an undesirable increase in the pressure drop. This is because the fins seek to enhance heat transfer by simply increasing surface area, which results in increased drag, therefore, pressure drop increase. Most of the improvement in heat transfer coefficient using fins is undermined by the increased pressure drop. For example, with serrated fins that result in an increase in the heat transfer coefficient of 10%, the cost of the pressure drop is 25%.
The heat recovery steam generator is a significant portion of the overall cost of the combined cycle power plant. By improving heat transfer efficiency within the heat recovery steam generator, the combined cycle power plant cost can be reduced.